A compressive optical image encryption method, which combines compressive sensing with phase-shifting interferometry on a joint transform correlator, is proposed in the fully optical domain. The object image is first permutated using a binary scrambling method. Next, the permutated object field is encrypted and registered as the holograms by phase-shifting interferometry on the joint transform correlator setup. Then, the encrypted images and the key are compressed to the compressed data using single-pixel compressive imaging. The original image can be reconstructed and decrypted using the specified algorithm. The simulations demonstrate that the method is effective and suitable for image security transmission.
A simple and practical color image encryption is proposed with the help of quick response (QR) code. The original color image to be encoded is firstly transformed into the corresponding QR code, and then a joint transform correlator encrypting architecture is used to encode the corresponding QR code into a positive ciphertext. In the decryption, the corresponding QR code can be restored with the correct decryption key, and hence the original color image can be retrieved without any quality loss by scanning the restored QR code with a smartphone. Compared with the reported color image encryption techniques, the proposed technique does not need to convert color image (RGB) into indexed image formats or segregate into three color components prior to encryption and hence the corresponding reverse processes also are not required after decryption. Moreover, with the help of the QR code, the proposed method has strong tolerance to speckle noise and other noises resulting from optical system. In addition, the proposed method is practical because its ciphertext is a positive image and can be printed directly or manufactured as a card. The feasibility and effectiveness of the proposed method are demonstrated by numerical results.
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